The invention refers to a device for working road surfaces according to the precharacterising part of claim 1, as well as a device for producing foamed bitumen for road machines according to the precharacterising part of claim 2.
Such devices are used, for example, in recycling machines for road construction. A road machine, in which the invention may be employed, is described in WO 96/24725, for example.
A device for producing foamed bitumen for road machines, comprising at least one mixing means having at least one expansion chamber, in which mixing means hot bitumen at a temperature of 180xc2x0 C. and water may be brought together via injection nozzles, is known from WO 95/22661. The device further comprises a heatable foaming reactor, as well as heatable supply and distributing lines, which lines may further be insulated. A plurality of nozzles are arranged side by side along a distributing line. A network of lines connects this distributing line to a central foaming reactor in which the bitumen foam is produced for all nozzles. Further, an agitating unit is provided in this foam reactor. It is a disadvantage of the known device that the bitumen foam has to go a long way from the expansion chamber to the nozzles. As a result, the foam decomposes partly on the way to the nozzles so that an exact dosing of the foamed bitumen is not possible, either. It is another problem that the known device is heated only partly and that in particular the nozzles are not heated. As a consequence, the cleaning of the apparatus is rather time-consuming. Since the cleaning is done with Diesel fuel, this additionally gives rise to a problem in disposing the contaminated fuel.
It is an object of the present invention to provide a device for working road surfaces, as well as a device for producing foamed bitumen for road working machines that allows for an exact dosing of the foamed bitumen and by which the cleaning and maintenance efforts are reduced to a minimum.
The object is solved with the features of claims 1 and 2.
Advantageously, the invention provides that in a device for working road surfaces, a means for producing foamed bitumen comprising a plurality of adjacent mixing means with foam outlet nozzles is arranged at the cover of the working roll so that the sprayed jet of foamed bitumen leaving the foam outlet nozzles is directed into the working chamber of the working roll and becomes mixed into the mixture of construction material granulated by the working roll. The hot bitumen is supplied from a bitumen reservoir via supply lines and a bitumen injection nozzle and is mixed in an expansion chamber of the mixing means with water supplied from a water reservoir via a water injection nozzle.
Injecting the foamed bitumen directly into the working chamber of the working roll is advantageous in that the foamed bitumen can be mixed directly into the granulated mixture of construction material, before the foam decomposes. The foamed bitumen is produced in a mixing means only shortly before it leaves the foam outlet nozzles, a separate mixing means being provided for each foam outlet nozzle. Producing foamed bitumen only just before it leaves from the foam outlet nozzles advantageously allows for an exact dosing of the foamed bitumen.
In the device for producing foamed bitumen, it is advantageously provided that the injection nozzle for hot bitumen has a plunger for the nozzle opening, which is adapted to the cross-sectional area of the nozzle and may be driven through a control to periodically clean or close the nozzle opening. For cleaning the nozzle, the plunger is pushed through the nozzle 1 to 2 times per minute so that the cross section of the nozzle is always kept free. When the nozzle is to be closed, the plunger remains in the cross section of the nozzle. Every nozzle may be addressed individually so that the working width may be selected, e.g., when passing over a road surface several times.
Further, in a device for producing foamed bitumen, it is provided that a microprocessor control controls the flow quantities of hot bitumen and water as a function of the advancement speed of the road machine. In this manner it is made sure that the dosing is effected with high precision and as a function of the traveling speed and that the ratio between foamed bitumen and granulated construction material is maintained constant.
In a preferred embodiment, it is provided that the water reservoir is provided on the running gear. It is an advantage of a water reservoir provided on the running gear that no separate water supply is required. The water in the water reservoir may also be used for other jobs, such as humidifying the ground, when compacting a road surface.
Preferably, it is provided that air may be blown additionally into the expansion chamber of each mixing means. An additional injection of air increases the forming of foam and allows for an expansion of the foamed bitumen to about 20 times the original volume. In an advantageous development, a mixing means with a foam outlet nozzle that may be separately switched on manually, the mixing means projecting laterally beyond the working roll. This additional foam outlet nozzle is intended for checking the quality of the foam at the beginning of the operation or during the operation of the road machine.
Preferably, the expansion chamber is circular in cross section, the bitumen injection nozzle being arranged coaxial with respect to the expansion chamber. The injection means or the blow means for the water and/or the air eject water or air radially or tangentially into the free jet of the hot foamed bitumen leaving the bitumen injection nozzle. This causes a strong turbulence in the expansion chamber, whereby an optimum foam quality may be obtained.
Preferably, the expansion chamber has an eccentrically arranged foam outlet nozzle. Such an eccentrically arranged nozzle increases the churning of the foamed bitumen and allows for a higher expansion coefficient and a longer half-life of the foam.
The mixing means may be heated by heating means (H). The heating is performed by thermostat-controlled heating means (H) that keep up the optimum working temperature prior to and during the operation, even in case of interruptions. A troublesome rinsing of the mixing means with the foam outlet nozzles can be omitted at the end of the working cycle.
The generator for generating the heating current generates the full heating voltage already when the drive motor is at idle and keeps the same constant even at higher numbers of rotations of the drive motor.
To this end, the generator has a hydraulic drive that may be adjusted to a constant rotational speed of the drive motor by means of a current control valve.
Further advantageous features are evident from the remaining subclaims.